I recently changed both knock sensors and wiring harness on my 99 Lexus rx 300! I purchased the parts on ebay and they state (OEM PARTS) Check engine, P0330,

Check you wiring harness, sometime the connectors are bad or corroded.

Did you replace the short wiring harness to the knock sensor, if not that is likely the cause of the issue.

You have 2 of them,here's a link showing where their at,once you get to page,click on switch and relay. SENSOR KNOCK CONTROL 176 07 Fits LEXUS RX300 1993 2005 Part 8961512090... Here's a video showing you where they are at. 2000 Lexus Es300 Knock Sensor Location Repair

Here's a link on replacing your knock sensor. RX300 knock sensor replacement DIY Club Lexus Forums

I had the same problem with my RX. Had both knock sensors replaced and the problem went away. Be sure to take it to a Tech that has a good scan tool so he can pull the codes and narrow down the problem, From what I understand a constant check engine light is usually not a big deal probably a sensor but a blinking light means major trouble. Take it to a shop that specializes in Toyota and Lexus.

I'm not a lexus guy , but I'm thinking that you have a vacuum leak somewhere.

sometimes the sensor it self goes bad and or the wire harness.cannot explain why but it happens on toyota's and lexus.

better get another mecanic as the motor is the same as a toyota 3.0 lv6....scary

Hello there..They are in the back of the engine block about in the middle of the motor..There might be one in the front of the engine in the middle of the block but most are in back.Hope this helps you and have a great day..

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_a3369546f8067589

Need to remove the upper and lower air intake manifold.  There are two knock sensors for the front and rear pistons banks.  If you plan to do this yourself it is about 1 to 2 hours.  While you are at it, there is a short coolant bypass hose sitting in the same spot, replace it.  Another problem with the knock sensor is the wire harness used to connect the two knock sensors into one connection sometimes wears out and contacts the metal on the engine causing false signals to the ECM, so replace this cable also.
Just did this last summer on my 99 ES300.  Pretty easy.
DIYr